Introduction & Objective: Diaphragmatic muscle that is responsible for the inhalation, innervations by right and left phrenic nerves. This nerve is a complex and feeds several part of mediastinum. The right phrenic is shorter than the left phrenic and arrived to diaphragm by traveling a different path than the left phrenic. In this study, we evaluated the origin, direction and right and left phrenic nerves and compared them with those offered in reference books and variations have been reported. Materials & Methods: This study was performed on 22 male and 2 female cadavers. We used simple dissect tools and observed tiny branches by the stereoscope. We evaluated the length of each nerve, relations in various areas, division of branches and terminal fibers. The presence or absence of accessory phrenic nerve was also assessed. For Statistical evaluation, the relevant parameters were recorded in tables. Mean (average) was measured by SPSS 16, and then the average of the sizes were compared. Results: In this study, we observed several variations on the left and right phrenic nerves from what was reported in the previous cases. Considerable differences were observed, in cases such as the pathway nerve of the neck to the chest and the presence of the anterior scalene muscle, passes through the diaphragmatic foramina, a multiple of right and left phrenic nerve branches, the presence or absence of accessory nerve and the phrenic nerve length. Our results showed that the increase in the length of the trunk, and ascending correlation to the left and right phrenic nerve elongation. With respected to the number of cadaver in this study, we showed that there is an accessory nerve in about 30% of the Iranian population. Conclusions: In this evaluation, we provided the different results about the pathway, branches, length and presence of accessory phrenic nerve. However, we found the same results of previous research. The neighborhood of this the nerve is important as in some cases, such as anesthesia and nerve block in the supraclavicular region or between scalenus muscles, the phrenic nerve also suffers from anesthesia. Also, the close proximity of this nerve and infraclavicular vein is very important in surgical operation related to this vein like canal catheter insertion. Since, the phrenic nerve is the only motor nerve of diaphragm, is important to be aware about how to spread the terminal branches of the nerve in the diaphragmatic muscle. Especially considering the fact that most of surgeries in the thoracic and mediastineum is associated with Communications and the organs adjacent to this nerve.